Putting hard drive reliability to the test shows not all disks are equal

Hitachi drives crush competing models from Seagate and Western Digital when it comes to reliability, according to data from cloud backup provider Backblaze. Their collection of more than 27,000 consumer-grade drives indicated that the Hitachi drives have a sub-two percent annualized failure rate, compared to three to four percent for Western Digital models, and as high as 25 percent for some Seagate units.

Hard drive manufacturers like to claim that their disks are extremely reliable. The main reliability measure used of hard disks is the mean time between failures (MTBF), and typically this is quoted as being somewhere between 100,000 and 1 million hours, or between 11 and 110 years.

These failures are generally assumed to follow a so-called bathtub curve, with relatively high failure rates when the drive is new—"infant mortality," caused by manufacturing defects—and similarly when the drive nears the end of its useful life, but low failure rates in between.

Data to actually support these beliefs, however, has always been a little scarce. Even when studies are published, the data within them is often anonymized. Backblaze's data names names and shows some big differences between the manufacturers.

The Hitachi disks are consistent performers. The Seagate ones are not.

Backblaze's data covers a range of drive models, capacities, and ages. In aggregate, the company has just under 40PB of Seagate storage, 36PB of Hitachi storage, and 2.6PB of Western Digital storage. The company has a few Samsung units (sold to Seagate in 2011) and Toshiba units, but too few to draw any meaningful conclusions.

Even from the same manufacturer there are some big differences. The least reliable drives are 1.5TB Seagate Barracudas that are nearing four years old on average, with an astonishing 25.4 percent annual failure rate. The newest Seagate drives, 4TB models, have a much more reasonable 3.8 percent annual failure rate. The units from Hitachi prove a lot more consistent, with the oldest drives, 2TB units averaging about three years old, having a failure rate of 1.1 percent, and the newest, 4TB units, having a 1.5 percent annual failure rate.

These numbers show just how useless the manufacturer's MTBF numbers can really be. Those 1.5TB Seagate drives are mostly split between two models. There are 539 model ST31500341AS Barracuda 7200.11 drives, which are specified by Seagate to have an annualized failure rate of 0.34 percent and an MTBF of 0.7 million hours, and there are 1929 model ST31500541AS Barracuda LP drives specified to have an AFR of 0.32 percent and an MTBF of 0.75 million hours.

Backblaze recorded AFRs of 25.4 percent and 9.9 percent respectively; substantially worse than the spec sheet number. However, there's a big difference. Backblaze's drives are operated 24/7. They're powered on all the time and aren't spun down or put to sleep by the system software using them. Seagate's AFR and MTBF numbers assume that the drives are powered on for only 2,400 hours each year, but conversely are spun down and backed up either 10,000 times per year (for the Barracuda 7200.11 units) or 50,000 times a year (for the Barracuda LP models).

Clearly, Seagate's usage model doesn't correspond at all to the way Backblaze uses the drives. These are consumer desktop drives, being used in a server scenario. However, it's not clear that Seagate's model corresponds very well with even desktop usage. For example, if you leave your desktop turned on 24/7, Seagate's MTBF number is irrelevant to you. If your desktop doesn't power down its hard drive when idle, Seagate's MTBF number is irrelevant to you. While there are sure to be some people who fit the assumptions, it's difficult to say that the specified MTBF actually represents typical usage.

In contrast, the company's enterprise-oriented disks calculate their AFRs and MTBFs assuming 8760 powered-on hours per year—which is to say, 24/7 operation. Even these have constraints, though, as they assume that only a certain amount of I/O is performed each year; do more than this amount, and the life of the disk may again be shortened.

In practice, it's likely that any large-scale collection of hard drive data is going to have these same discrepancies, leaving little good way to evaluate the accuracy of MTBF specs for desktop drives. The people using hard disks in bulk are going to be those operating data centers, not desktop systems. The use of consumer drives isn't unusual, due to their lower pricing, and clearly the drives do work well enough in servers.

The Western Digital drives do show an early drop followed by a leveling out. The Seagates for some reason show a big dip at 20 months.

Another feature of the Backblaze data is that it doesn't consistently show the bathtub curve. The Western Digital drives do appear to show a bathtub curve, with an initial burst of failures followed by long-term reliability, but neither the Seagate nor Hitachi drives appear to do the same.

Though backups are always important, none of this means that owners of Seagate drives should crack open their PCs and rush to replace their drives. Backblaze notes that its conditions are pretty hostile. Two particular kinds of drives, Western Digital 3TB units and Seagate LP (low power) 2TB units, suffered extreme failure rates. However, the company believes that this is primarily due to the level of vibration in their drive cages which pack 45 disks into a 4U case, combined with both drives being energy-efficient models that aggressively spin down when not in use. These things are less likely to be an issue in regular desktop machines.

Even with the higher failure rate, Backblaze says that it is still buying Seagate drives, as they're cost-effective for the company's RAID usage. It might not be best to run out and buy Hitachi drives for their reliability, either. Hitachi sold its drive business to Western Digital last year, and Western Digital subsequently sold the 3.5 inch drive division to Toshiba, and it's too soon to know whether this has had any impact on their longevity.

209 Reader Comments

headline note: the annual rates are not up to 24% - the only 24% figure in the report is for a 3-year failure rate.

EDIT: After reading the source report, there's actually one model of Seagate drive that had a 120% failure rate, and another that did have a 25% annual rate. The number of these drives used is relatively tiny, but those rates are staggering.

I had to have my Seagate 1.5TB drive replaced five times within the warranty period. The drives would typically last around a month before they'd either start throwing up SMART errors or just die with no warning. I spent more time in the Seagate RMA process than I did actually using the drives.

I just bought a Seagate drive after the last four Western Digitals I have owned all died at around the 4-year mark. I was used to replacing drives at the 5-year mark in my home PC, and had never had a drive die before that (even my IBM Deathstar), so was disappointed at that failure record and decided to switch brands. I'm second guessing that now.

Damn, and I always avoided Hitachi drives because they were IBM Deathstar's back in the day. I should have figured Hitachi would have fixed that all up long ago.

Sounds like these models were not based on the DeskStar drives, but they picked and chose the pieces that worked. Good for them - I haven't though about Hitachi drives in a long time. Sounds like I'll have to take another look.

There's one thing about the article that seems to be missing: the definition of "failure". I do note that the underlying blog post eventually answers this - it's errors to the point of rejection by the RAID. This could be many CRC errors, or a refusal to spin. Some drives spend time in a bucket called "troubled" before failing. In this metric, it mirrors the failure rate.

I just ordered a Seagate drive :-( 4TB NAS version though. Planning to use it as offline backup against the possibility of ransomware, so who knows what sort MTBF you get sitting on a shelf. Is "sticktion" still an issue? I will power it up every once in a while.

Damn, and I always avoided Hitachi drives because they were IBM Deathstar's back in the day. I should have figured Hitachi would have fixed that all up long ago.

I would have thought IBM fixed that line... it was only one range of HDDs, after all; it's not like IBM suddenly forgot how to manufacture HDDs ever again.

The changes in Seagate's failure rates over time most likely reflect changes in manufacturing or materials... so the dip in the middle of the graph needn't be considered that odd. Also isn't it a bit soon to see bathtub curves appear anyway? It's only a 3 year timespan.

And they do fail. I've seen some drives with close to a 24% failure rate. I work in a field that works very close with disks and data.

Folks just don't understand.

harddrives are fragile and RAID 5 isn't a backup, it's simply a window for "oh shit, get this data on tape".

EDIT: Something about this I would want to know is if the same disks stay in the same racks or if other brands go into those racks. I'd want to know if there was any hardware pattern noted or even looked for accross the failures.

Damn, and I always avoided Hitachi drives because they were IBM Deathstar's back in the day. I should have figured Hitachi would have fixed that all up long ago.

Yeah, exactly. And I used to be a Seagate's fan, but I did notice a couple of years ago a very high failure rate and I switched to WD drives. But I am really surprised. I haven't though high of Hitachi's drives.

Oh, and I wonder what's Seagate reaction to this will be, assuming there will be reaction, because this is all over the major tech news sites. This looks really bad for Seagate.

And they do fail. I've seen some drives with close to a 24% failure rate. I work in a field that works very close with disks and data.

Folks just don't understand.

harddrives are fragile and RAID 5 isn't a backup, it's simply a window for "oh shit, get this data on tape".

If you're using RAID as a backup, you're doing it wrong. It was never intended to be used that way. And when you do a backup, never ever choose a backup media that has the same failure rate as your primary storage.

The real issue with Seagates that has kept me from using them over the past few years is that their RMA process is byzantine and awful.

Also, this data is cool and all... but WD bough Hitachi's storage division for $4.3B two and a half years ago, so those drives are no longer really available. You can still buy "HGST" branded drives from WD for the time being, but it's clear that they're winding down those assembly lines, just like Maxtor sold their own drives and Quantum-derived drives side-by-side for a few years, and Seagate sold their own drives and Maxtor-derived drives simultaneously as well.

It might not be best to run out and buy Hitachi drives for their reliability, either. Hitachi sold its drive business to Western Digital last year, and it's too soon to know whether this has had any impact on their longevity.

Funny enough, I run a mix of 2Tb Seagate LP and 4Tb HGST drives in my own arrays (Storage Spaces these days), and the only disk that I have had fail in a number of years was an HGST, which died just a couple of months ago. That said, they did replace it under warranty and the process was very smooth.

I have always been surprised after the Deskstar 75GXP and, to a lesser extent, 60GXP fiasco, how many people completely swore off IBM hard drives. They made reliable hard drives before, and they eventually solved the 75GXP and 60GXP issues with firmware updates (though they were too late for most of the drives that had already been sold). The RMA replacement for my 60GXP which was shipped to me with the fixed firmware still works. The 120GXP on up weren't any less reliable than anything else. If I boycotted a manufacturer of just about anything that made a model or two with high failure rates I don't think I'd be able to buy anything at all.

Hmm. I have 8 Seagate 1.5TB 341AS's, that have been spinning for 4.1 years in a extremely hostile and warranty voiding environment. Ambient temperatures of -35C to 40C (-31F to 104F) and fans with no temperature control .. 0 failures. ;-) As it happens they just started reallocating bad sectors a week or so ago. Right on cue.

And here I thought it was just a coincidence that Seagate reduced the warranty period on their hard drives to only one year...

When looking at drives, if the warranty is less than 3 years I refuse to buy it. A one year warranty on a spinning platter tells you they have absolutely no confidence in their quality control.

Yeah, any time a hard drive manufacturer drops their standard warranty, it should be a huge red flag. If they don't trust their product, you shouldn't either.

Every time hard drive manufacturers cut their warranties, quality inevitably has suffered in the name of continually increasing capacity. 2003 comes to mind, when Seagate, WD, IBM, and Maxtor all simultaneously slashed their standard warranty from three years to one, leaving only Samsung standing firmly behind their product... Turns out, Samsung was the only company who wasn't selling junk. I refused to buy anything except Samsung for years afterward, and I was extremely sad when Seagate gobbled them up a few years ago.

The great thing about those 1.5TB 341AS's is the 5-year warranty that Seagate provided. Now that Seagate Barracuda only come with 1 year warranty I buy WD instead - similar price for a longer warranty.

It might not be best to run out and buy Hitachi drives for their reliability, either. Hitachi sold its drive business to Western Digital last year, and it's too soon to know whether this has had any impact on their longevity.

Actually, the Hitachi 3.5" business got spun off to Toshiba; WD kept everything else. So the Toshiba 3.5" drives you're seeing for sale now are likely re-badged Hitachi drives, and the Hitachi branded ones will no longer be available once current stock clears out of the distribution channel.

I have 2 Maxtor HDD's that have been working for over 10 years. I had a much newer WD and a Toshiba both bite the dust after little more than a year

I've used a Maxtor HDD from the early '90s that worked the last time I tried it. But a Seagate drive I used a few years ago failed after only a few months, and this makes it evident that it wasn't because of butterfly farts. Just shockingly bad.

how kind of you ars to post this article 2 hours after i ordered and payed for two WD 3TB external drives , my last WD 2TB died 1 month ago after 2 years and 8 month . however there are no good firewire or tb hdd for a reasonable price (have 3 old firewire hdd going on 7+ years). So my question becomes do the high failure rate of WD 3TB only relate to the rack mounted drives or all WD 3TB drives??